1. Field of the Invention
The present inventio relates to electrical interlock apparatus for electrical equipment, and more specifically, to electrical switch interlock apparatus for metal-enclosed switchgear which disconnects electrical components within the switchgear automatically by opening a door over the access opening to the switchgear before human access is possible.
2. Description of the Prior Art
Metal-enclosed switchgear is well known in the art. Typically, such switchgear is utilized in electrical distribution systems for large buildings, factories, subdivisions, portions of subdivisions, etc. Such switchgear typically may include transformers, fuses, interrupter switches, electrical switches, and other such electrical components necessary for the electrical distribution system.
The switchgear typically comprises a metal enclosure having one or more doors or overlying access openings into the interior portions of the enclosure where the components are situated. Since the electrical components typically are electrically charged, such metal-enclosed switchgear ordinarily have lock arrangements to preclude unauthorized access and vandalism.
In addition, the switchgear also may utilize a double-door arrangement whereby a solid outer door overlies an inner screen door overlying the access opening into the switchgear. Thus, the outer door may be opened without opening the inner screen door to permit visual observation of the component while precluding accidental contact with the energized component within the enclosure. Thus, the inner screen door prevents the accidental or blundering type of accidental contact with energized components which could be a hazard to the serviceman or operator.
Often, in such metal-enclosed switchgear, potential transformers and high voltage potential transformer fuses are situated within the switchgear and protected behind the hinged screen door. It is desirable to gain access to the fuses to remove them in order to isolate the potential transformer from the high voltage circuit so that service can be performed. The removal and handling of such potential transformer fuses would be accomplished, of course, with insulated tools or other apparatus and equipment to protect the lineman from direct contact with the high voltage energized components. However, if the potential transformer happens to be loaded such as by supplying current to heaters or other instruments, a hazardous electrical arc may result when the fuse is removed from the mounting. Further, in certain circumstances, the potential transformer may inadvertently become energized from its low voltage side if a maintenance man happens to connect a 120 volt power source to, for example, one of the components normally connected to the low voltage side during component testing.
Accordingly, it would be a desirable advance in the art to provide an electrical switch interlock arrangement which automatically disconnects the electrical components within the switchgear when the door is opened so that accidental shock or damage to the equipment is avoided. The present invention provides a new and unique electrical switch interlock for electrical equipment which solves the problems presently existing in the prior art.